There is known a container that includes a lid member coupled to a container body by a hinge so as to be openable/closable relative to an opening portion of the container body. FIG. 5 shows a cross section of such a container 900. In the container 900, a lid member 911 is closed in such a way that a sidewall 922 and an inner ring 912 provided to the lid member 911 sandwich an opening portion of a container body 901. At this time, in order to enhance sealing properties, the inner ring 912 is fitted to an inner peripheral surface of the opening portion of a sidewall 902 of the container body 901. The sidewall 922 of the lid member 911 has an inner peripheral surface on which a projection 914 is formed along the circumferential direction. The sidewall 902 of the container body 901 has an outer peripheral surface on which a recess 903 is formed along the circumferential direction. In the state where the lid member is closed, the projection 914 and the recess 903 are engaged with each other to lock the lid member 911 so as not to be opened.